1. Field of the Invention
The present invention relates generally to positioning apparatus for displacing a movable member to a desired position relative to a support, and more particularly to improved servoactuator apparatus for accurately positioning such movable member relative to a support angularly about either or both of two axes in response to an electrical command signal.
2. Description of the Prior Art
Conventional hydraulic actuators for positioning a swivelled load, such as an antenna, a mirror, a gun, a rocket engine, a telescope, or the like, have included a piston and cylinder operatively arranged to impart translational motion to an end of a radius arm located remote from the effective pivot point. Two of such actuators have been used, each arranged ninety degrees from the other, to create a two-axis positioning system. Such known forms of two-axis hydraulic actuators have been used to control aximuth and elevation, pitch and yaw, or the like.
Alternatively, rotary hydraulic actuators have been used in such positioning systems. However, these rotary actuators generally include internally-moving parts, such as pistons, gears, vanes, and the like.
A two-axis positioner should, desirably, be highly accurate and have high dynamic response characteristics. Upon information and belief, these desired degrees of accuracy and dynamic response have been heretofore limited by several factors, such as backlash in mechanical couplings, friction in such couplings, compliance of such couplings, and fluid compliance due to its compressibility under load. Inasmuch as these factors serve to limit system accuracy and dynamic response, it is generally desired to minimize or eliminate such factors to maximize total system performance.